Telephone system



Aug 8a 1 TELEPHONE SYSTEM Filed Deo. l, 1952 l ,2 7 /4 7]"-V 3 2LJ- 0 LVN n l 9 j l 6 I F/Gil J OPI?- TEL.

/NVENTOR A T Toms/gy` Patented Aug. 8, 1933 UNITED lla'lr"m11"-A oFFlc-e A TELEPHONE Y Edward E. Hinrichsen, New York, N. Y., assigner to Bell Telephonev Laboratories, 'Incorporated,V` f YNew York, N.-Y., afCorporation cf New York VAppncarit ilieeanbei1,1932'.l serial No. 645,195

y '6 claims. .(01. 179-42) This invention relates to telephone systems and more particularly to operators cord circuits used at private branch exchange switchboards.

An annoying ieature of private branch exchange operation is thatwhen a call comes in on a trunk line from a central oiiice to the private branch exchange while the` private branch exchange operator is busy, she will often plug into the trunk jack in order to retire the signal but will delay answering the call. With the usual type of circuit now in use plugging :into the trunk by the answering operator cuts off the ringing signal to the calling subscriber at the central oice and, where automatic registration is used in the central office, charges up the call to thecalling subscribers line. The subscribenhowever, has no indicationv that his call is receiving l attention and the'ringing signal is usually cut oi so quickly in a case of this kind that heV is likely not to notice it and may think .that the call has not been completed to the private branch exchange and accordingly hangs up andv calls again. y Y f An object of the invention is to prevent effecting anyoperation of apparatusassociated with the outgoing end'of a trunk circuit extending from a central oice to a private branch ex' change switchboard until the private branch operator has plugged into the answering jackfof the vtrunk and operated the listening key associated with the cord circuit employed.`

Another object is to prevent retirement vof the kline signal, when the operator plugs into, the vanswering jack, until the Vlistening key is operated and the operator speaks intol her transmitter.

Still another object is to give theoperator at the private branch exchange a signal, independent ofthe line signal, when she plugs into acalling line and to maintain this signal displayed until rshe operates the listening key and speaks vinto her transmitter. y

A'feature of the invention resides in normally maintaining anopen circuit between the answering plug of the private branch exchange cordy and the remainder of the cord circuitapparatus, and closing this' circuit only when the listening key is operated, and further, in locking this circuit closed independent of the listeningkey when the operator speaks intoher transmitter.

Another feature resides in retiring the line signal of a callingrline only when the listening key, of acord connected to the line, has-heen operated and the'operator has spoken into her transmitter.

VStillV another feature resides inv displaying a pilot signal whenever the answeringy plug fof. a

cord is inserted in a calling line jack and Vretir- A which remains *lightedl until the operator has actuated her` listening keyand spoken into her transmitter; and Y `Fig.- Zrepresents an alternative modication kof the arrangement of Fig. 1 inv which the line lamp of theA calling line is not extinguished when the, answering plug is inserted in the jack, but instead remains lighted until the operator has actuated her llistening, key and spoken into her transmitter.

` The operation of Fig. 1 is as follows: Let it be assumed that 1 is a calling line indicated by a line signal, not shown. When the operator notes the line signal she plugs ananswering plug 2' of one of her cord circuits into the` answering jack k3 of the calling line whereupon the line signal is retired in thejwell-known manner and pilotlamp 4 which is common to her position-is lighted.

the operator that she hasplugged into a calling line but has not yet answered, until the operator is ready to answer the call at which time she actuates her listening key 9 which in addition to connecting her telephone set tothe cord circuit in use. also closes a, circuit to operate relay 1,0 which vvcan b'etraced from ground, winding of cut-off 4relay 8 associated with the calling line, sleeves of jack 3 and plug 2, contactfll of the listening key 9,.'winding ofrelay 10, contacts 12 of relay'? and 1 the normal contacts ofthe voice frequencyrelay 13 to battery.' It will `be noted that another path to battery exists through the Winding of relay '7, but insuiiicient Vcurrent flows therein at this time, due to the direct path just'traced, to cause this relay to operate.

v Relay 10 in Operating closes the tip and ring to the answering plug 2 thereby completing a conconductors 14 and 15 of the cord circuit through nection between the operators telephone set and the calling line.

The connection of the cord circuit conductors 14 and 15 to the calling line set up the usual bridge condition on the line and in the case of a central oiiice trunk line cause certain apparatus at the central ofce to perform such functions as tripping the ringing automatically, register the respond and break its normally closed armature contact thereby opening the direct path .to battery previously traced for the operation of relay 10. This removal of the shunt path around relay 7 permits current to flow therethrough and causes it to operate which opens contacts 6 and 12 and closes contacts 16. When contact 6 opens relay 5 releases and extinguishes pilot lamp ll. The opening of contacts 12 introduces a break in the shunt path around relay 'l so that when the contacts of relay 13 are later closed, relay 7 will not be shortcircuited and released. Closure of contact 1670i relay 7 completes a locking circuit whereby relays '7 and 1G are held up in series with each other under the sole control of the sleeve of thek plug'2 and consequently the cord circuit is now permanently locked to the calling line at contacts of relay independent of the listening key and can only be released by removing plug 2 from jack 3. From the foregoing it will be observedl that the pilot lamp 4 was lighted when the operator plugged into the jack 3, that the cord circuit conductors were connected to the plug 2 when the operator actuated the listening key and that the pilot lamp was extinguished and the cord circuit locked to the calling line independent of the listening key when the operator responded by speaking into her transmitter.

The operation of Fig; 2 differs only slightly from that of Fig. 1. When the operator observes the lighted .line lamp 1'7 caused by operation of linerelay 18 she inserts the answering plug 19 into jack 20. This act performs no other function at this time as it will be observed that the sleeve circuit is open at the contact 2l of listening key 22. Cut-off relay 23, therefore, remains inert and contrary to the usual practice the line lamp 1'7 continues to glow as a warning to the operator that she has not yet handled the call.

. When the operator actuates listening key 22 she connects her telephone set across the tip and ring conductors 24 and 25 of the cord and closes contact 21 whichV completes the following circuit: Ground, winding of cut-off relay 23, sleeves of jack 26 and plug 19, contact 21, winding of relay 27 and high resistance 28 to battery. Resistance 28 and the resistance of relay 27 are so chosen that the current iiowing in this circuit is sufcient to operate relay 27, but insuicient to operate the usual low resistance cut-off or sleeve relay 23.

Operation of relay 27 closes at its contacts 29 and 30 the tip and ring conductors 24 and 25 of the cord due to the answering plug 19 thereby completing a connection between the cperators telephone set and the calling line exactly as described under Fig. l.

The operator may now respond by the usual salutation thereby generating voice currents the circuit of Fig. 2 provides for keeping the line which operate the voice frequency relay 31 connected across her telephone circuit.

Operation of relay 3l connects ground at its armature and contact to a circuit which can be traced through resistance 32, contacts 33 of relay 27 which were closed when this relay operated in response to actuation of the listening keyycontact 3e and winding of relayV 35 to battery. Relay 35 operates in this circuit thereby opening contacts 36 and closing contacts 37 which remove the high resistance from the circuit including relays 23 and 27 and substitute therefor the relatively low resistance winding of relay 35. This lowering of the resistance of the circuit from ground through relays 23, 27 and 35 permits sufficient current to flow through the cut-oif sleeve relay 23 to cause it to operate thereby releasing line relay 18 and opening the circuit for line lamp 17 which is therefore extinguished.

Whenrelay operates in response to operation of relay 31 it closes its lower contact 38 thereby completing a locking circuit independent of the contacts 2l of listening keyV 22, for relays 23, 2'7 and 35. This circuit may be traced from ground, relay 23, sleeves of jack 26 and plug 19, f

contacts 38 of relay 35, winding of relay 27, contacts 37 of relay 35 and winding of that relay to battery.

This circuit it will be observed is under sole control of the sleeve contacts ci plug 19 and jack 26 and these relays therefore remain operated and the cord circuit locked in the answering plug until the plug is removed from the line jack.

From the foregoing it will be understood that lamp of the calling line lighted until the operator hasractuated her listening key and spoken into her transmitter whereupon the line lamp is extinguished and the cord circuit is locked'to the answering plug and consequently to the calling line independent of the listening key Vand under sole control of the answering plug.

What is claimed is: f

1. In an operators cord circuit, means jointly controlled by insertion of the answering plug into an answering jack andl operation of the operators listening key to electrically connect the cord circuit with the answering plug thereof and means operated by voice: current in the operators circuit to lock said cord circuit connected to the answering plug independent of said listening key.`

2. In a telephone system, a calling line, an operatorscord circuit including an answering plug normally disconnected therefrom but connected a to said calling line, an operators telephone circuit, switching means for connecting said operators circuitto said cord circuit, relay means voperated in response to operation of said switching means for connecting said plug and lcord circuit, and means responsive to voice current in said operators circuit'for locking said relay means operated independent of said switching means.

3. In a telephone system, a calling line, an

answering plug connected to said line, an op- '140 erators cord circuit associated with said plug `but normally disconnected therefrom, an operators telephone circuit, a listening key for connecting the operators circuit to the cord circuita relay responsive to operation of said key for connecting saidplug and cord circuit, a second relay adapted when operated to .lock up in series with said rst relay independent o said key, and Voice operated means responsive to voiceV frequency current in said operators circuit for initially operating said second relay.

4. In a telephone system, a Vcalling line,v an A normally disconnected therefrom, an operators telephone circuit, a listening key for connecting the operators circuit to the cord circuit, relay means responsive to operation of said key for connecting said plug and cord circuit, a second relay means adapted when operated to retire said signal and lock up in series with said iirst means independent of said key and voice operated means responsive to voice frequencyrcurrents in said operators circuit for initially operating said second relay means.

5. In a telephone system, a calling line, a line signal cut-olf relay in the sleeve circuit thereof, an answering plug connected to said line, an operators cord circuit associated with said plug but normally disconnected therefrom, an operators telephone circuit, a listening key for connecting the operators circuit to the cord circuit, a relay for connecting said plug and cord` circuit responsive to'actuation of said key,` a second relay adapted when operated to operate said cut-off relay and to lock itself up in series with said first relay independentof said key, and voice operatedr means responsive to voice frequency currents in said operators circuit for initially operating said second relay. I j

6. In a telephone system, a calling line, a line signal cut-off relayin the sleeve circuit thereof, an answeringplug connected to said line, an operators cord circuit associated with said plug but normally disconnected therefrom, an operatorsv telephone circuit, a listening key for connecting the operators circuit to the cord circuit, a rst relay for connecting said plug and cord circuit, a

low resistance relay, a circuit for said first relay including a high resistance, a normal contactY of .the low resistance relay, contacts of said listening key and the sleeve conductor of the cord circuit including said cut-off relay, said circuit being closed to operate vsaid first relay when said key is actuated and said resistance being of such Value as to prevent operation of said cut-off relay in series therewith, said low resistance relay voice frequency currents in said operators circuit for initially operating said second relay.

EDWARD E. HINRICHSEN. 

